Tom Emerson from Symantec recently posted the following useful information about problems with THINK C 5.0.3:

"As many have found, THINK C 5.0.3's global optimizer has several serious bugs that did not exist in version 5.0.2. We are currently addressing these and hope to have a fix available in the near future. In the interim we ask that if you must use 5.0.3 do not use the code motion global optimization. Bugs have been reported (new in 5.0.3, non-existent in 5.0.2) in the handling of volatile (a volatile expression will be optimized out; this is linked to the code motion) and the align_arrays pragma (doesn't work in several cases)."